SANTA CLARA (CBS SF) — As the number of people being tested for COVID-19 continues to decline, Santa Clara health officials say testing is even more important now that new variants of the virus are beginning to spread.

The health officials plea comes as the attention of most local residents has switched from testing to getting an appointment for a vaccine shot.

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But earlier this week, Santa Clara officials confirmed they have detected the county’s second case of B1351, also known as the South African variant. The case, which was reported in early March, is believed to have resulted from community transmission.

It is the fourth confirmed case of B1351 reported in California so far.

“This latest case confirms that we do have community transmission, and reminds us to not let down our guard in the middle of this pandemic,” said Santa Clara County Public Health Director Dr. Sara Cody.

The health department also said the number of cases from variant B117, also known as the U.K. or British variant, has increased to 15 in Santa Clara County. Officials cautioned the true level of spread is not known since they can only perform genomic sequencing on only a fraction of the cases.

Officials in Contra Costa County have also announced their first two cases of B117.

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On Saturday, Santa Clara County health officials urged local residents to continue to be tested.

“The more we can track the virus and its variants, the better equipped we are to protect ourselves,” said Dr. Marty Fenstersheib, the county’s COVID-19 Testing and Vaccine Officer. “Testing has always been a critical part of our pandemic response and it remains an important tool today. With these variants spreading in our community, each person who may have been exposed should be tested. It is the key to breaking the chain of transmission.”

Health officials said that testing remains free, easy and available seven-days-a-week. Among the options are appointment or walk-in, drive-through or walk-up, and specimen collection by nasal swab or saliva.

Frontline workers should get tested at least once a month and up to once every two weeks, officials said, and continue testing even after being vaccinated.

Appointment-based testing continues at the Santa Clara County Fairgrounds, with rotating appointment-only city sites this upcoming week in Sunnyvale, Morgan Hill, Santa Clara, Los Altos and Milpitas. Walk-ins continue to be accepted at standing pop-up sites in Gilroy and San José. Mobile testing buses will be in Campbell, San José, and Alviso.

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Appointments can be made starting seven days in advance of the testing date until all slots are reserved at www.sccfreetest.org.